The present invention relates to polyacetal resin compositions which can be used to make fragrance-emitting shaped articles, and to fragrance-emitting shaped articles such as slide fasteners. More specifically, the invention relates to polyacetal resin compositions which can be used to make fragrance-emitting shaped articles that retain the characteristics inherent to polyacetal resins, such as excellent mechanical properties, heat resistance, fatigue resistance, sliding resistance and chemical resistance, and to shaped articles made from such compositions.
Aromas are believed to have a healing effect on the mind by acting on the brain through the sense of smell. For example, much attention has been devoted recently to the relaxing and refreshing effects that can be achieved using aromatherapy.
Fragrances also have the effect of counteracting unpleasant odors. Techniques that have been widely used to this end include the use of fragrances as deodorants, which chemically react with the odoriferous molecules responsible for an unpleasant odor, as masking agents which overwhelm and in essence xe2x80x9chidexe2x80x9d the unpleasant odor, and as modifiers which alter the nature of an odor, such as perfumes that modify body odors and make them appealing.
A large range of products have been developed for the purpose of achieving such effects. Even in the technical field relating to plastic shaped articles, fragrance-emitting shaped articles have been produced by the addition of fragrances to resin compositions. One such example is disclosed in JP-B 61-15827
Fragrance-emitting products have been developed also in the form of various types of fasteners widely used in garments and other applications. For example, JP-A 7-111,903 discloses a type of fastener in which a specific low-boiling fragrance material has been directly impregnated into the fabric pieces on the loop side and/or hook side of the fastener.
Polyacetal resins are produced by polymerization primarily from formaldehyde monomer or from a starting material composed principally of trioxane, which is a formaldehyde trimer. Because of their excellent mechanical properties such as tensile strength and rigidity, and their excellent fatigue resistance, sliding resistance and chemical. resistance, polyacetal resins are widely used in a variety of mechanical parts, electrical and electronics components, sliding parts and mechanisms for automotive and other applications, and fasteners.
However, polyacetal resins are exposed to high temperatures and placed in a molten state during melt processing operations such as extrusion or injection molding, at which time thermal degradation (such as thermal depolymerization) may arise. Such thermal degradation generates an irritating formaldehyde odor during extrusion or injection molding or from the shaped article, which can adversely affect the working environment and become an obstacle to the work itself. Moreover, formaldehyde may accumulate within the shaped articles, compromising the properties of the finished product.
Many solutions have been proposed for reducing the decomposition of polyacetal resins when molten and suppressing the amount of formaldehyde generated, or for reducing the formaldehyde odor that arises from shaped articles during solidification and cooling.
For example, JP-A 8-41288 discloses a polyacetal resin composition which includes an active imino group-bearing organic cyclic compound so as to lower the concentration of formaldehyde released from the polyacetal resin.
When, however, an aldehyde group-bearing fragrance material of the type disclosed in the foregoing publication, such as vanillin or dibenzalsorbitol, is added to a polyacetal resin for the purpose of imparting a fragrance to shaped articles such as fasteners manufactured from the resin, the aldehyde group-bearing fragrance material reacts with the formaldehyde that arises in the polyacetal resin during processing to produce formic acid. The formic acid accelerates thermal degradation of the molten polyacetal resin, further increasing the pungent formaldehyde odor.
Also, the addition to the polyacetal resin of a fragrance material having a boiling point lower than the melt processing temperature of the polyacetal or the composition results in the melting or vaporization and release of the fragrance during the extrusion or injection molding operation. The fragrance may then be too strong, becoming instead an unpleasant odor, or may form an unpleasant odor in association with formaldehyde released due to thermal degradation of the polyacetal resin during the processing operation. In either case, the results include a decline in the quality of the work environment and a reduction in the fragrance-emitting effect of the shaped article.
Therefore, one object of the invention is to provide a shaped article capable of emitting a desired fragrance while retaining the excellent properties inherent to polyacetal resins, such as mechanical properties, heat resistance, fatigue resistance, sliding resistance and chemical resistance, which shaped article preferably has a minimal concentration of formaldehyde. Another object of the invention is to provide a resin composition which can be used to make such shaped articles. A further object of the invention is to provide a method of manufacturing such shaped articles.
It has been discovered that adding a fragrance material having an aldehyde group-free chemical structure to the polyacetal resin makes it possible to provide shaped articles which emit a desired fragrance while yet retaining the excellent properties inherent to polyacetal resins, such as mechanical properties, heat resistance, fatigue resistance, sliding resistance and chemical resistance.
Accordingly, the invention provides a polyacetal resin composition comprising a polyacetal resin and a fragrance material having an aldehyde group-free chemical structure.
In the foregoing polyacetal resin composition of the invention, the fragrance material preferably has a boiling point which is at least as high as the polyacetal resin processing temperature.
In either of the foregoing polyacetal resin compositions of the invention, the fragrance material preferably has a chemical structure which includes a functional group that reacts with aldehyde groups in the polyacetal resin.
In any one of the foregoing polyacetal resin compositions of the invention, the content of the fragrance material, based on the overall weight of the resin composition, is preferably 0.001 to 1.0% by weight.
Any of the foregoing polyacetal resin compositions of the invention preferably also includes 0.001 to 5% by weight of a formaldehyde scavenger, based on the overall weight of the resin composition. The formaldehyde scavenger may be one which chemically fixes formaldehyde in the cooling step during processing of the resin composition, and also at normal temperature.
Another embodiment of the invention provides a fragrance-emitting shaped article made from any one of the foregoing polyacetal resin compositions.
The fragrance-emitting shaped article of the invention is manufactured from the foregoing polyacetal resin composition. The composition includes a fragrance material that may contain a functional group reactive with aldehyde groups in the polyacetal resin, or that may contain 0.001 to 5% by weight of a formaldehyde scavenger (based on the overall weight of the resin composition) wherein the formaldehyde scavenger chemically fixes formaldehyde in the cooling step during shaping of the resin composition, and also at normal temperature. The concentration of formaldehyde released from the resulting shaped article is not more than 25 ppm at normal temperature.
A further embodiment of the invention provides a slide fastener chain, wherein a row of engaging teeth is shaped from any one of the foregoing resin compositions.
A still further embodiment of the invention provides a slide fastener wherein any one or more members from the group consisting of a row of engaging teeth, a slider, a top end stop and a bottom end stop is shaped from any one of the foregoing resin compositions.
An additional embodiment of the invention provides a slide fastener wherein a separable end stop assembly comprising a pivot pin, a box pin and a box is shaped from any one of the foregoing resin compositions.
Yet another embodiment of the invention provides a method of manufacturing fragrance-emitting shaped articles, which method comprises incorporating a fragrance material having an aldehyde group-free chemical structure when making the polyacetal resin-containing shaped article.
The shaped articles of the invention, typical examples of which include the slide fasteners described above, emit a fragrance and are thus capable of serving as a pleasant aromatic source while retaining the outstanding mechanical properties, heat resistance, fatigue resistance, sliding resistance, chemical resistance and other characteristics inherent to polyacetal resins. The further addition of a formaldehyde scavenger enables the production of shaped articles which have even better aromaticity and suppress the release of formaldehyde.
The invention also provides resin compositions from which such shaped articles can be produced, and a method of manufacturing shaped articles that emit fragrance more effectively.